The present invention relates to a method for setting a given temperature in the temperature range below 0.degree.C at a sample, particularly for setting a given moisture content in a gas at dew points in such temperature range, and to an apparatus for practicing the method.
In order to be able to perform certain types of experiments, such as, for example, sintering experiments with oxidic nuclear fuels in gas atmospheres having a defined low moisture content, it is necessary to employ devices which permit a defined and reproduceable setting of a moisture content for a measuring gas having a dew point in the range between -30.degree. and -65.degree.C. Studies of the properties of oxidic nuclear fuels such as UO.sub.2 -- PuO.sub.2 for fast breeder reactors have demonstrated the necessity for being able to set a defined oxygen/metal ratio in the oxide on the basis of the moisture content of a hydrogen-containing measuring gas.
It is known to set given moisture contents in a gas, for example in air-conditioning systems by initially continually humidifying the gas and then extracting moisture therefrom, for example in a cooling trap, until the desired residual moisture content has been obtained.
It is also known to set given temperatures in the range below 0.degree.C at a sample with the aid of cooling devices such as, for example, refrigerators, low temperature cryostats or Peltier cells and to control these cooling devices by means of thermostats.
Significant drawbacks of these known methods and apparatuses are the high costs for the apparatus involved, the relatively large space requirement, the relatively high operating costs, the large moisture and ice quantities that must be converted, and the corresponding large structural size required for the humidifying and freezing devices.